This disclosure relates generally to online systems, and in particular to selection and presentation of content on an online system.
An online system, such as a social networking system, allows users to connect to and communicate with other online system users. A user creates a profile on an online system that is tied to its identity and includes information about the user, such as interests and demographic information. Additionally, the online system receives or generates content items associated with one or more users. For example, the online system receives advertisements from one or more users, generates stories describing actions performed by one or more users, or receives information describing events attended by one or more users. The online system maintains the content items and presents users with one or more content items when the users access the online system.
Presenting commercial content items, such as advertisements, to users allows the online system to obtain revenue by charging advertisers when a user views or interacts with a commercial content item associated with an advertiser. Similarly, presenting non-commercial content items, such as stories or status updates, promotes user engagement with the online system. Increasing user engagement with the online system increases the number of opportunities to obtain revenue by presenting users with commercial content items, such as advertisements.
Presenting a user with content items more relevant to the user (i.e., presenting the user with higher-quality content items) increases both revenue for the online system and user interaction with the online system. Conventionally, online systems use a content selection system applying targeting or filtering rules to various content items for selecting content items to present to a user. For example, the content selection system ranks content items through an auction process or other suitable process. The content selection system selects content items for presentation during a latency period, which begins when a request for content is received by the online system and ends when the selected content items are presented to a user. The duration of the latency period depends on one or more content selection parameters, such as the number of advertisements to be ranked and may also depend on changes in traffic on the online system. Various factors may affect the traffic on the online system, such as time of day, occurrence of events, unexpected events, or other factors causing fluctuations in the demand placed on computing resources of the online system.
While the quality of content selected for presentation generally increases as the number of content items evaluated by the online system's content selection process increases, the latency period also increases for evaluating the increased number of content items using limited computing resources of an online system during periods of high user demand. Thus, when the online system evaluates a large number of content items, the quality of presented content items improves, while system performance declines. Because limited computing resources evaluate content items, increasing the number of content items evaluated causes a decline in system performance, which results in a long latency period, system delays and possible network time-outs. Conversely, if the online system evaluates a small number of content items, the latency period is shorter, which improves system performance, while the quality of presented content declines. This variation in latency period and content quality degrades a user's overall experience with a conventional online system, which undermines an online system's potential for increased user engagement and revenue.